Rotary driving device and image forming apparatus

ABSTRACT

A rotary driving device includes a rotary shaft supported rotatably about an axis thereof on a predetermined supporting member, a rotary load body mounted on the rotary shaft to project radially outward from the rotary shaft in such a manner that the rotary load body can rotate integrally with the rotary shaft about the axis thereof, a driver for rotating the rotary shaft about the axis thereof, a disk mounted on the rotary shaft coaxially therewith for integral rotation with the rotary shaft, the disk having a mounting hole formed therein, a pendulum loosely fitted in the mounting hole, and an adjustment mechanism for adjusting a relative position relationship between a central axis position of the mounting hole and a center of gravity position of the pendulum under conditions where the disk is rotating.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/616,742 filed on Sep. 14, 2012, which in turn is a divisional of U.S.patent application Ser. No. 12/466,478 filed on May 15, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary driving device having a rotaryload body which is driven to rotate integrally about a rotary shaft. Thepresent invention also relates to an image forming apparatus providedwith such a rotary driving device.

2. Description of the Related Art

Japanese Laid-open Patent Publication No. 2002-195348 describes anexample of a conventional rotary driving device which is applied to animage forming apparatus. The rotary driving device of this Publicationincludes a rotary body system for rotatably supporting a rotary body, adriving system having an electric motor serving as a rotary drivingsource for driving the rotary body system to rotate, and adriving/transmission system interconnecting the rotary body system andthe driving system.

The rotary body system includes a rotary shaft on which the rotary bodyis so mounted as to be able to rotate integrally with the rotary shaftand a centrifugal pendulum vibration absorber which is so mounted on therotary shaft as to be able to rotate integrally therewith. The rotaryshaft is rotatably supported by a structural part like a frame viabearings. When the electric motor is actuated, the rotary shaft, therotary body and the centrifugal pendulum vibration absorber rotatetogether as a single structure.

The centrifugal pendulum vibration absorber is provided for absorbingvibration of the rotary body which rotates integrally with the rotaryshaft on a common axis, and is configured to include a disk which is somounted on the rotary shaft as to be able to rotate integrallytherewith, a plurality of circular holes formed in the disk to passtherethrough at equal intervals along a circumferential direction of thedisk and cylindrical pendulums loosely fitted in the individual circularholes.

When the rotary body rotates as a result of actuation of the electricmotor in the centrifugal pendulum vibration absorber thus configured,the pendulums loosely fitted in the individual circular holes oscillatetherein while producing pendular motion along inner surfaces of thecircular holes. Vibrational energy produced by rotation of the rotarybody is absorbed by the pendular motion (oscillatory motion) of thependulums, so that the rotary body is kept from vibrating.

Provided that the aforementioned centrifugal pendulum vibration absorberis so configured that there is a difference L between the radius of eachcircular hole in the disk and that of each pendulum, the center of thedisk is separated from the center of each circular hole by a distance Rand the disk rotates at an angular velocity ω, a natural frequency ω_(n)of vibration of each pendulum is known to be given by the followingequation:ω_(n) =ω√{square root over (R/L)}

On the other hand, an actual frequency of vibration of the rotary bodyobserved when the rotary body rotates at the angular velocity ω can bedetermined by calculation or from an experiment. Therefore, it ispossible to match the natural frequency of vibration of each pendulumwith the frequency of vibration of the rotary body by substituting avalue of the actual frequency of vibration of the rotary body for ω_(n)in the aforementioned equation and properly setting values of L and R sothat the equation is satisfied. Under conditions where the naturalfrequency of vibration of each pendulum is matched to the frequency ofvibration of the rotary body, vibration produced when the rotary bodyrotates at the angular velocity ω is effectively absorbed by theoscillatory motion of the pendulums in theory.

In the rotary driving device of Japanese Laid-open Patent PublicationNo. 2002-195348, however, even if the difference L between the radius ofeach circular hole in the disk and that of each pendulum and thedistance R between the center of the disk and the center of eachcircular hole are determined based on the aforementioned equation sothat the natural frequency ω_(n) of vibration of each pendulum matchesthe frequency of vibration of the rotary body, and the circular holesare formed in the disk and the pendulums are adjusted according thesetting of and L, there can be a case where a desired vibrationabsorbing effect can not be obtained due to errors in design ormanufacture when the rotary body is actually rotated.

Also, if it is found that an appropriate vibration absorbing effect isnot obtained after the circular holes are formed in the disk, it may benecessary to manufacture a new disk to achieve an intended result.Making a new disk would however results in increasing cost.

SUMMARY OF THE INVENTION

The invention is intended to provide a solution to the aforementionedproblems of the prior art. Specifically, it is an object of theinvention to provide a rotary driving device which can produce animproved vibration absorbing effect by properly adjusting vibrationabsorbing performance and contribute to a reduction in manufacturingcost by avoiding a waste of a disk once mounted on a rotary body forabsorbing vibration. It is another object of the invention to provide animage forming apparatus provided with such a rotary driving device.

According to the present invention, a rotary driving device includes arotary shaft supported rotatably about an axis thereof on apredetermined supporting member, a rotary load body mounted on therotary shaft to project radially outward from the rotary shaft in such amanner that the rotary load body can rotate integrally with the rotaryshaft about the axis thereof, a driver for rotating the rotary shaftabout the axis thereof, a disk mounted on the rotary shaft coaxiallytherewith for integral rotation with the rotary shaft, the disk having amounting hole formed therein, a pendulum loosely fitted in the mountinghole, and an adjustment mechanism for adjusting a relative positionrelationship between a central axis position of the mounting hole and acenter of gravity position of the pendulum under conditions where thedisk is rotating.

These and other objects, features and advantages of the invention willbecome more apparent upon a reading of the following detaileddescription along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a basic structure of a rotarydriving device according to the invention.

FIG. 2 is a front view of a centrifugal pendulum vibration absorbershown for explaining a natural frequency of vibration of a centrifugalpendulum.

FIGS. 3A and 3B are perspective views of a centrifugal pendulumvibration absorber according to a first embodiment of the invention,FIG. 3A being an exploded perspective view and FIG. 3B being aperspective assembly view.

FIGS. 4A and 4B are cross-sectional views taken along lines IV-IV ofFIG. 3B, FIG. 4A showing a state in which a stationary disk element anda movable disk element are most separated from each other and FIG. 4Bshowing a state in which the stationary disk element and the movabledisk element are located closest to each other.

FIGS. 5A and 5B are perspective views of a centrifugal pendulumvibration absorber according to a second embodiment of the invention,FIG. 5A being an exploded perspective view and FIG. 5B being aperspective assembly view.

FIGS. 6A and 6B are cross-sectional views taken along lines VI-VI ofFIG. 5B, FIG. 6A showing a state in which each of truncated conicalbodies is most separated from a rotary shaft and FIG. 6B showing a statein which each of the truncated conical bodies is located closest to therotary shaft.

FIG. 6C is a fragmentary perspective view cut away along lines VI-VI ofFIG. 5B.

FIGS. 7A and 7B are perspective views of a centrifugal pendulumvibration absorber according to a third embodiment of the presentinvention, FIG. 7A being an exploded perspective view and FIG. 7B beinga perspective assembly view.

FIGS. 8A and 8B are cross-sectional views taken along lines VIII-VIII ofFIG. 7B, FIG. 8A showing a state in which each of spherical bodies isset at a position most separated from the rotary shaft and FIG. 8Bshowing a state in which the spherical bodies are located closest to therotary shaft.

FIG. 9 is a perspective view showing the external appearance of oneexample of an image forming apparatus according to the invention.

FIG. 10 is a frontal cross-sectional view showing the internalconstruction of the image forming apparatus of FIG. 9.

FIG. 11 is a perspective view showing an example of a driving system ofa photosensitive drum and the centrifugal pendulum vibration absorberapplied to the photosensitive drum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view showing a basic structure of a rotarydriving device 1 according to the present invention. As shown in FIG. 1,the rotary driving device 1 includes a rotary shaft 2 mounted rotatablyabout an axis thereof between two frames (supporting member) F, acylindrical rotary load body 3 which is fitted on the rotary shaft 2 toprotrude radially outward therefrom along the entire circumference ofthe rotary shaft 2 so that the rotary load body 3 can rotate integrallywith the rotary shaft 2 about the axis thereof, a driving motor (driver)4 for rotating the rotary shaft 2 about the axis thereof, and acentrifugal pendulum vibration absorber 5 fitted on the rotary shaft 2so that the centrifugal pendulum vibration absorber 5 can rotateintegrally with the rotary shaft 2 on the same axis therewith.

There is provided a gear mechanism 4 a between the driving motor 4 andthe rotary shaft 2. A driving force of the driving motor 4 istransmitted to the rotary shaft 2 via the gear mechanism 4 a, causingthe rotary shaft 2 to rotate.

The centrifugal pendulum vibration absorber 5 includes a disk 6 fittedon the rotary shaft 2 on the same axis therewith so that the disk 6 canrotate integrally with the rotary shaft 2, a plurality of circularmounting holes 7 formed in the disk 6 at equal intervals along acircumferential direction of the disk 6, and centrifugal pendulums(pendulums) 8 loosely fitted in the individual mounting holes 7. Whilethe disk 6 has four mounting holes 7 formed therein in the illustratedbasic structure, the number of the mounting holes 7 is not limited tofour but may be less than or more than four.

FIG. 2 is a front view of the centrifugal pendulum vibration absorber 5shown for explaining a natural frequency of vibration of eachcentrifugal pendulum 8. The disk 6 rotates about the rotary shaft 2 andFIG. 2 shows a state in which the centrifugal pendulums 8 are positionedradially most outward in the respective mounting holes 7 due to acentrifugal force produced by rotation of the disk 6 about the rotaryshaft 2.

Provided that the centrifugal pendulum vibration absorber 5 shown inFIG. 2 is so configured that a center axis position C1 of each mountinghole 7 is separated from a center axis position C of the disk 6 by adistance R, a center position O1 of each centrifugal pendulum 8 isseparated from the center axis position C1 of the pertinent mountinghole 7 by a distance L under conditions where an outer peripheralsurface of each centrifugal pendulum 8 is in contact with an innerperipheral surface of the pertinent mounting hole 7, the disk 6 rotatesat an angular velocity ω, and each centrifugal pendulum 8 has a naturalfrequency ω_(n) of vibration, there is a relationship expressed by thefollowing equation as previously mentioned:ω_(n) =ω√{square root over (R/L)}  (1)

When the frequency of vibration of the rotary driving device 1determined by gear meshing conditions, eccentricity of the rotary loadbody 3 and cogging or the like of the driving motor 4 is known, thecentrifugal pendulum vibration absorber 5 will be brought into a statein which the centrifugal pendulums 8 completely absorb vibration of therotary driving device 1 by setting the frequency of vibration of therotary driving device 1 to be equal to the natural frequency ofvibration of the centrifugal pendulums 8.

Therefore, the centrifugal pendulum vibration absorber 5 exhibits amaximum vibration absorbing effect if the aforementioned equation issatisfied, that is, by substituting the frequency of vibration of therotary driving device 1 for ω_(n) and the angular velocity of the disk 6for ω in equation (1) above and setting values of R and L so thatequation (1) is satisfied. Even though the values of R and L are so set,however, the value of ω_(n) will not become equal to the frequency ofvibration of the rotary driving device 1 if a dimensional error occursin any of the mounting holes 7 or if the frequency of vibration of therotary driving device 1 can not be exactly determined. Consequently, itwill become impossible for the centrifugal pendulum vibration absorber 5to exhibit a sufficient vibration absorbing effect in this case.

To cope with the aforementioned problem, the rotary driving device 1 ofthis embodiment is configured such that the centrifugal pendulumvibration absorber 5 has an adjustment mechanism 9 which makes itpossible to vary the distance R between the center axis position C1 ofeach mounting hole 7 and the center axis position C of the disk 6.

Centrifugal pendulum vibration absorbers 51, 52, 53 according to firstto third embodiments of the invention having different types ofadjustment mechanisms 9 are described hereinbelow with reference toFIGS. 3A to 8B.

First Embodiment

FIGS. 3A and 3B are perspective views of the centrifugal pendulumvibration absorber 51 according to the first embodiment, FIG. 3A beingan exploded perspective view and FIG. 3B being a perspective assemblyview. FIGS. 4A and 4B are cross-sectional views taken along lines IV-IVof FIG. 3B, FIG. 4A showing a state in which a stationary disk element611 and a movable disk element 612 are most separated from each otherand FIG. 4B showing a state in which the stationary disk element 611 andthe movable disk element 612 are located closest to each other.

As shown in FIGS. 3A and 3B, the centrifugal pendulum vibration absorber51 of the first embodiment includes a disk 61 having a dual-diskstructure and a plurality of spherical bodies (pendulums) 81 fitted inmounting holes 71 formed in the disk 61.

The disk 61 includes the stationary disk element 611 which is mounted onthe rotary shaft 2 in such a manner that the stationary disk element 611is kept from moving along an axial direction of the rotary shaft 2 andthe movable disk element 612 which is so mounted on the rotary shaft 2to be movable along the axial direction on the right side of thestationary disk element 611 as illustrated in FIGS. 3A and 3B. Thestationary disk element 611 has an inner cylindrical part 611 aprojecting from a right surface of the stationary disk element 611 on acommon axis therewith (as illustrated in FIGS. 3A and 3B), and themovable disk element 612 has an outer cylindrical part 612 a projectingtherefrom on a common axis therewith. The inside diameter of the innercylindrical part 611 a is made slightly larger than the outside diameterof the rotary shaft 2, so that the rotary shaft 2 is passed through theinner cylindrical part 611 a in sliding contact therewith.

The inside diameter of the outer cylindrical part 612 a is made slightlylarger than the outside diameter of the inner cylindrical part 611 a, sothat the outer cylindrical part 612 a can be fitted on the innercylindrical part 611 a in sliding contact therewith. The innercylindrical part 611 a and the outer cylindrical part 612 a are formedto have approximately the same length. Also, as illustrated in FIGS. 3Aand 3B, the amount of leftward projection of the outer cylindrical part612 a from the movable disk element 612 is made slightly smaller thanthe diameter of each spherical body 81.

In the inner cylindrical part 611 a, there is formed a through hole 611b passing radially through the inner cylindrical part 611 a. Also, therotary shaft 2 has a threaded hole 21 radially tapped therein at anappropriate position. On the other hand, in a portion of the outercylindrical part 612 a projecting rightward from the movable diskelement 612, there is formed a slot 612 b extending along an axialdirection of the outer cylindrical part 612 a and passing therethrough.

After aligning the slot 612 b with the through hole 611 b, the outercylindrical part 612 a of the movable disk element 612 is fitted on theinner cylindrical part 611 a of the stationary disk element 611. Then,after fitting the rotary shaft 2 into the inner cylindrical part 611 aso that the threaded hole 21 aligns with the through hole 611 b, a screw(locking member) B is screwed into the threaded hole 21 through the slot612 b and the through hole 611 b, whereby the stationary disk element611 is kept from moving along the axial direction. On the other hand,the movable disk element 612 can be moved back and forth along the axialdirection of the rotary shaft 2 within a particular movable rangedefined by the slot 612 b.

Therefore, the movable disk element 612 is fixed to the rotary shaft 2when the screw B is fastened after setting a desired distance betweenthe stationary disk element 611 and the movable disk element 612 bymoving the movable disk element 612 back and forth along the rotaryshaft 2.

In the stationary disk element 611 and the movable disk element 612,there are formed at their surface the aforementioned plurality (four ineach disk element 611, 612 in this embodiment) of mounting holes 71 atequal intervals along a circumferential direction so that the mountingholes 71 in the stationary disk element 611 align with those in themovable disk element 612. The mounting holes 71 formed in the stationarydisk element 611 are hereinafter referred to as stationary disk elementside mounting holes (first mounting holes) 711 and the mounting holes 71formed in the movable disk element 612 are hereinafter referred to asmovable disk element side mounting holes (second mounting holes) 712.

As shown in FIGS. 4A and 4B, each of the stationary disk element sidemounting holes 711 formed in the stationary disk element 611 has agenerally trumpet-like cross-sectional shape gradually increasing indiameter toward an opposing surface of the movable disk element 612.Similarly, each of the movable disk element side mounting holes 712formed in the movable disk element 612 has a generally trumpet-likecross-sectional shape gradually increasing in diameter toward anopposing surface of the stationary disk element 611. The stationary diskelement side mounting holes 711 and the movable disk element sidemounting holes 712 are formed to have the same dimensions.

There is provided an adjuster 613 between the stationary disk element611 and the movable disk element 612 while fitted on the innercylindrical part 611 a. The adjuster 613 of this embodiment is made ofsoft synthetic resin foam. Under conditions where the outer cylindricalpart 612 a of the movable disk element 612 is fitted on the innercylindrical part 611 a of the stationary disk element 611 and set inposition by tightening the screw B, the adjuster 613 is caused toelastically deform by compression. As a consequence, the adjuster 613exerts an elastic force which serves to hold the movable disk element612 in a stably mounted state.

The spherical bodies 81 are made to have a diameter slightly larger thana minimum inside diameter of each of the mounting holes 711, 712.Therefore, when fitted in the respective mounting holes 711, 712, thespherical bodies 81 are sandwiched between the stationary disk element611 and the movable disk element 612 as shown in FIGS. 4A and 4B and,thus, the spherical bodies 81 will not come out of the mounting holes711, 712.

In the centrifugal pendulum vibration absorber 51 of the firstembodiment, an adjustment mechanism 9 a for adjusting a relativeposition relationship (i.e., the distance L shown in FIGS. 4A and 4B)between a center axis position C1 of each mounting hole 71 and a centerposition O1 (i.e., the center of gravity) of the corresponding sphericalbody 81 is configured with the movable disk element 612 which can bemoved back and forth along the axial direction of the rotary shaft 2 andthe screw B for keeping the movable disk element 612 from moving alongthe axial direction.

The centrifugal pendulum vibration absorber 51 of the first embodimentthus configured makes it possible to freely set the distance between thestationary disk element 611 and the movable disk element 612 byloosening the screw B and removing the same from the threaded hole 21and through hole 611 b of the inner cylindrical part 611 a so that thestationary disk element 611 and the movable disk element 612 are in adesired state between the state shown in FIG. 4A in which the stationarydisk element 611 and the movable disk element 612 are most separatedfrom each other and the state shown in FIG. 4B in which the stationarydisk element 611 and the movable disk element 612 are located closest toeach other.

When the distance between the stationary disk element 611 and themovable disk element 612 is maximized as shown in FIG. 4A, a distance Sbetween the center O1 of each spherical body 81, positioned radiallyoutward due to a centrifugal force produced by rotary motion of thecentrifugal pendulum vibration absorber 51 around the rotary shaft 2,and a center axis C of the rotary shaft 2 takes a maximum value S1. Onthe other hand, when the distance between the stationary disk element611 and the movable disk element 612 is minimized as shown in FIG. 4B,the distance S between the center O1 (the center of gravity) of eachspherical body 81 and the center axis C of the rotary shaft 2 takes aminimum value S2.

The above-described arrangement of the first embodiment makes itpossible to arbitrarily set the distance S between the center O1 of eachspherical body 81 and the center axis C of the rotary shaft 2 in therange between the maximum value S1 and the minimum value S2 underconditions where the centrifugal pendulum vibration absorber 51 rotatesby moving the movable disk element 612 within the movable range thereofback and forth along the axial direction of the rotary shaft 2. Thismeans that vibration absorbing performance of the centrifugal pendulumvibration absorber 51 can be corrected, if inappropriate, by fineadjustment of the distance S between the center O1 of each sphericalbody 81 and the center axis C of the rotary shaft 2 performed byadjusting the distance between the stationary disk element 611 and themovable disk element 612 on a trial-and-error basis.

Second Embodiment

FIGS. 5A and 5B are perspective views of the centrifugal pendulumvibration absorber 52 according to the second embodiment, FIG. 5A beingan exploded perspective view and FIG. 5B being a perspective assemblyview. FIGS. 6A and 6B are cross-sectional views taken along lines VI-VIof FIG. 5B, FIG. 6A showing a state in which each of truncated conicalbodies 82 is most separated from the rotary shaft 2 and FIG. 6B showinga state in which each of the truncated conical bodies 82 is locatedclosest to the rotary shaft 2. FIG. 6C is a fragmentary perspective viewcut away along lines VI-VI of FIG. 5B.

As shown in FIGS. 5A and 5B, the centrifugal pendulum vibration absorber52 of the second embodiment includes a generally thick-walled partiallyhollowed disk 62 which is fixedly fitted on the rotary shaft 2 on acommon axis therewith, the partially hollowed disk 62 having a pluralityof cutout spaces (cavities) 65 formed therein as will be describedlater, a plurality (four in this embodiment) of mounting holes 72 formedin the partially hollowed disk 62 at equal intervals along acircumferential direction thereof, the aforementioned plurality oftruncated conical bodies (pendulums) 82 fitted in the correspondingmounting holes 72, and adjustment mechanisms 9 b for adjusting arelative position relationship (i.e., the distance L) between a centeraxis position C1 of each mounting hole 72 and a center axis O2 (FIGS. 6Aand 6B) of the corresponding truncated conical body 82.

The partially hollowed disk 62 has a cylindrical projecting part 621protruding rightward from a right surface of the partially hollowed disk62 as illustrated in FIG. 5A, as if passing through the partiallyhollowed disk 62 at a center position thereof. The inside diameter ofthe cylindrical projecting part 621 is made slightly larger than theoutside diameter of the rotary shaft 2, so that the rotary shaft 2 canbe passed through the cylindrical projecting part 621 in sliding contacttherewith. In the cylindrical projecting part 621, there is formed athrough hole 622 passing radially through the cylindrical projectingpart 621 so that a screw B can be fitted in the through hole 622. Whenthe screw B is tightly screwed into the threaded hole 21 in the rotaryshaft 2 through the through hole 622, the partially hollowed disk 62 canrotate integrally with the rotary shaft 2 about the axis thereof.

The partially hollowed disk 62 has the aforementioned plurality ofcutout spaces or cavities 65 which are formed by cutting out portions ofthe partially hollowed disk 62 inward toward the mounting holes 72 froman outer peripheral surface of the partially hollowed disk 62 atlocations corresponding to the corresponding mounting holes 72. Thesecutout spaces 65 are for fitting the truncated conical bodies 82 whichwill be described later in detail. On the right surface of the partiallyhollowed disk 62 (as illustrated in FIG. 5A), there are formed aplurality of bushes 651 protruding rightward at locations correspondingto the respective cutout spaces 65. These bushes 651 serve to supportlater-described adjusting screws 92 in a stable state.

As illustrated in FIG. 5A, each of the truncated conical bodies 82 isshaped such that a right end surface has a minimum diameter and a leftend surface has a maximum diameter, so that each of the truncatedconical bodies 82 diminishes from the left end surface to the right endsurface, forming a tapered circumferential surface 821. The maximumdiameter of each truncated conical body 82 (i.e., the diameter of theleft end surface of each truncated conical body 82 shown in FIG. 5A) ismade slightly smaller than the diameter of each mounting hole 72 and thethickness of each truncated conical body 82 is made approximately equalto that of the partially hollowed disk 62.

In the second embodiment, a pair of ring-like stopper plates 66 arescrewed to the partially hollowed disk 62 on both sides as shown in FIG.5B for closing off the individual mounting holes 72 to prevent thetruncated conical bodies 82 fitted in the mounting holes 72 from comingoff. In this configuration, each truncated conical body 82 fitted in themounting hole 72 is allowed to freely move in a direction perpendicularto an axial direction (i.e., in a radial direction) within the mountinghole 72 under conditions where movement of each truncated conical body82 in the axial direction within the partially hollowed disk 62 isrestricted by the pair of ring-like stopper plates 66.

Each of the adjustment mechanisms 9 b includes an adjusting tab 91fitted in the pertinent cutout space 65 such that the adjusting tab 91can move back and forth along a thickness direction of the partiallyhollowed disk 62, the aforementioned adjusting screw 92 serving as amoving member for moving the adjusting tab 91 back and forth in thecutout space 65 along the thickness direction of the partially holloweddisk 62, the adjusting screw 92 being fitted in the pertinent cutoutspace 65 passing through the bush 651 and the adjusting tab 91, and anE-ring 93 fitted on a left end of the adjusting screw 92 (as illustratedin FIGS. 6A and 6B) so that the adjusting screw 92 will not come offunder conditions where the adjusting screw 92 is passed through thepartially hollowed disk 62.

Each of the adjusting tabs 91 has a generally rectangular shape in frontview as shown in FIG. 5A. Each adjusting tab 91 has a thicknessapproximately one-quarter of the thickness (left-to-right dimension asillustrated in FIGS. 6A and 6B) of each cutout space 65 and a width(i.e., a circumferential dimension measured when each adjusting tab 91is fitted in the pertinent cutout space 65) slightly smaller than thecircumferential dimension of the cutout space 65. An end surface of eachadjusting tab 91 facing the center of the partially hollowed disk 62 isshaped to form a tapered peripheral surface 911 which remains in contactwith the tapered circumferential surface 821 of the pertinent truncatedconical body 82. Also, each adjusting tab 91 has a threaded hole 912formed therein into which the adjusting screw 92 is screwed.

Under conditions where each adjusting tab 91 fitted within the pertinentcutout space 65 with the tapered peripheral surface 911 facing thecenter of the partially hollowed disk 62, the adjusting screw 92 isinserted into the cutout space 65 through the bush 651 and tightenedinto the threaded hole 912 in the adjusting tab 91. The adjusting screw92 passes to the outside of the partially hollowed disk 62 through ahole formed in a wall surface of the partially hollowed disk 62 locatedon an opposite side of the bush 651 of each cutout space 65. The E-ring93 is fitted on that part of the adjusting screw 92 which protrudes tothe outside of the partially hollowed disk 62. Consequently, theadjusting screws 92 are screwed into the respective adjusting tabs 91 tosupport the adjusting tabs 91 and thus fitted in the partially holloweddisk 62 in such a manner that the adjusting screws 92 will not come off.

When the partially hollowed disk 62 rotates on the rotary shaft 2, acentrifugal force produced by the rotary motion of the partiallyhollowed disk 62 causes the truncated conical bodies 82 to move radiallyoutward within the respective mounting holes 72 so that the taperedcircumferential surfaces 821 of the truncated conical bodies 82 go intocontact with the tapered peripheral surfaces 911 of the respectiveadjusting tabs 91.

The centrifugal pendulum vibration absorber 52 of the second embodimentthus configured makes it possible to move each adjusting tab 91, intowhich the adjusting screw 92 is screwed, back and forth within thecutout space 65 along the thickness direction of the partially holloweddisk 62 by turning the pertinent adjusting screw 92 clockwise andcounterclockwise about an axis thereof. The above-described arrangementof the second embodiment makes it possible to set the adjusting tabs 91at a desired position between the state shown in FIG. 6A in which eachadjusting tab 91 is located most rightward and the state shown in FIG.6B in which each adjusting tab 91 is located most leftward.

When each adjusting tab 91 is located most rightward, the taperedperipheral surface 911 of each adjusting tab 91 is in contact with aright part of the tapered circumferential surface 821 of the pertinenttruncated conical body 82 so that the truncated conical body 82 is setat a position most separated from the rotary shaft 2.

On the other hand, when each adjusting tab 91 is located most leftward,the tapered peripheral surface 911 of each adjusting tab 91 is incontact with a left part of the tapered circumferential surface 821 ofthe pertinent truncated conical body 82 so that the truncated conicalbody 82 is set at a position closest to the rotary shaft 2.

Since the centrifugal pendulum vibration absorber 52 of the secondembodiment makes it possible to easily vary the distance between thetruncated conical bodies 82 and the rotary shaft 2 by moving theadjusting tabs 91 back and forth, it is possible to find a position ofeach truncated conical body 82 best suited for obtaining desiredvibration absorbing performance on a trial-and-error basis.

Also, since the positions of the truncated conical bodies 82 can beadjusted individually, it is possible to perform a fine adjustment forobtaining the desired vibration absorbing performance compared to a casewhere all of the centrifugal pendulums 8 are adjusted likewise as awhole.

Third Embodiment

FIGS. 7A and 7B are perspective views of the centrifugal pendulumvibration absorber 53 according to the third embodiment, FIG. 7A beingan exploded perspective view and FIG. 7B being a perspective assemblyview. FIGS. 8A and 8B are cross-sectional views taken along linesVIII-VIII of FIG. 7B, FIG. 8A showing a state in which each of sphericalbodies 81 is set at a position most separated from the rotary shaft 2and FIG. 8B showing a state in which the spherical bodies 81 are locatedclosest to the rotary shaft 2.

As shown in FIG. 7A, the centrifugal pendulum vibration absorber 53 ofthe third embodiment includes a single thick-walled disk 63 which isfixedly mounted on the rotary shaft 2 on a common axis therewith, aplurality (four in this embodiment) of conical holes (mounting holes) 73formed in the thick-walled disk 63 at equal intervals along acircumferential direction thereof, the aforementioned plurality ofspherical bodies (pendulums) 81 fitted in the respective conical holes73, and an adjustment mechanism 9 c for adjusting a relative positionrelationship between a center axis position C1 of each conical hole 73and a center position O1 (i.e., the center of gravity) of thecorresponding spherical body 81.

The thick-walled disk 63 has a cylindrical projecting part 631protruding rightward from a right surface of the thick-walled disk 63 asillustrated in FIG. 7A, as if passing through the thick-walled disk 63at a center position thereof. The inside diameter of the cylindricalprojecting part 631 is made slightly larger than the outside diameter ofthe rotary shaft 2, so that the rotary shaft 2 can be inserted throughthe cylindrical projecting part 631 in sliding contact therewith. In thecylindrical projecting part 631, there is formed a through hole 632passing radially through the cylindrical projecting part 631 so that ascrew (locking member) B can be fitted in the through hole 632. When thescrew B is tightly screwed into a threaded hole 21 in the rotary shaft 2through a slot 942 formed in a later-described outer cylindrical part(projecting part) 941 and the through hole 632, the thick-walled disk 63can rotate integrally with the rotary shaft 2 about the axis thereof.

Each of the conical holes 73 has a generally trumpet-likecross-sectional shape gradually increasing in diameter from a left sideof the thick-walled disk 63 to a right side thereof as illustrated inFIG. 7A. An inner peripheral surface of each conical hole 73 is shapedto form a tapered circumferential surface 731.

The diameter of each spherical body 81 is made slightly larger than aminimum diameter of each conical hole 73 on a left side thereof asillustrated in FIGS. 8A and 8B. Therefore, the spherical bodies 81 willnot come off leftward from the conical holes 73.

The adjustment mechanism 9 c includes a positioning disk 94 forpositioning the spherical bodies 81 under conditions where the sphericalbodies 81 fitted in the respective conical holes 73 are kept from comingoff leftward as illustrated in FIG. 7A, and the aforementioned screw Bfor fixing the positioning disk 94 to the rotary shaft 2 through thethrough hole 632 in the cylindrical projecting part 631.

The positioning disk 94 has the aforementioned outer cylindrical part941 projecting rightward therefrom on a common axis with the positioningdisk 94 as illustrated in FIGS. 7A and 7B. The inside diameter of theouter cylindrical part 941 is made slightly larger than the outsidediameter of the cylindrical projecting part 631. Therefore, when theouter cylindrical part 941 is fitted over the cylindrical projectingpart 631, the positioning disk 94 can be moved back and forth along adirection in which the cylindrical projecting part 631 extends.

The aforementioned slot 942 is formed in the outer cylindrical part 941of the positioning disk 94 to extend in an axial direction thereof at alocation corresponding to the through hole 632 in the cylindricalprojecting part 631. With the outer cylindrical part 941 of thepositioning disk 94 fitted on the cylindrical projecting part 631 of thethick-walled disk 63, the rotary shaft 2 is inserted into thecylindrical projecting part 631. Then, with the slot 942 in the outercylindrical part 941, the through hole 632 in the cylindrical projectingpart 631 and the threaded hole 21 in the rotary shaft 2 aligned with oneanother, the screw B is passed through the slot 942 and the through hole632 and screwed into the threaded hole 21. As a consequence, thecentrifugal pendulum vibration absorber 53 of the third embodiment isassembled as illustrated in FIG. 7B.

In the third embodiment, an adjuster 613 like that of the firstembodiment is placed between the thick-walled disk 63 and thepositioning disk 94. This arrangement serves to mount the positioningdisk 94 in position to the thick-walled disk 63 in a stable state.

In the centrifugal pendulum vibration absorber 53 of the thirdembodiment thus configured, the positioning disk 94 can be moved backand forth along the axial direction of the rotary shaft 2 within aparticular movable range defined by the slot 942 in the outercylindrical part 941 upon loosening the screw B. When the centrifugalpendulum vibration absorber 53 rotates about the rotary shaft 2integrally therewith under conditions where the positioning disk 94 islocated most rightward as illustrated in FIG. 8A, the spherical bodies81 fitted in the respective conical holes 73 move along the taperedcircumferential surfaces 731 thereof and are positioned most outward inradial directions due to a centrifugal force produced by the rotarymotion of the centrifugal pendulum vibration absorber 53. In thiscondition, the difference L between the center axis position C1 of eachconical hole 73 and the center position O1 (i.e., the center of gravity)of the corresponding spherical body 81 takes a maximum value.

On the other hand, when the centrifugal pendulum vibration absorber 53rotates about the rotary shaft 2 integrally therewith under conditionswhere the positioning disk 94 is located most leftward as illustrated inFIG. 8B, the individual spherical bodies 81 are forced leftward by thepositioning disk 94 and thus positioned most inward along the radialdirections in the respective conical holes 73. In this condition, thedifference L between the center axis position C1 of each conical hole 73and the center position O1 (i.e., the center of gravity) of thecorresponding spherical body 81 takes a minimum value (“0” in theillustrated example of FIG. 8B).

The above-described arrangement of the third embodiment makes itpossible to freely set each spherical body 81 at a desired positionbetween the position most separated from the rotary shaft 2 as shown inFIG. 8A and the position closest to the rotary shaft 2 as shown in FIG.8B by moving the positioning disk 94 back and forth along the axialdirection of the rotary shaft 2. If the screw B is tightened underconditions where each spherical body 81 has been set in the desiredposition in the aforementioned fashion, the positioning disk 94 properlypositioned relative to the thick-walled disk 63 is held stably mountedthereto.

As thus far described in detail, the rotary driving device 1 accordingto the foregoing embodiments includes the rotary shaft 2 mountedrotatably about the axis thereof between the predetermined frames F, therotary load body 3 which is fitted on the rotary shaft 2 to projectradially outward therefrom so that the rotary load body 3 can rotateintegrally with the rotary shaft 2 about the axis thereof, the drivingmotor 4 for rotating the rotary shaft 2 about the axis thereof, and thecentrifugal pendulum vibration absorber 5 fitted on the rotary shaft 2so that the centrifugal pendulum vibration absorber 5 can rotateintegrally with the rotary shaft 2 on the same axis therewith as shownin FIGS. 1 and 2.

The centrifugal pendulum vibration absorber 5 includes the disk 6 inwhich the mounting holes 7 are formed to pass therethrough at equalintervals along the circumferential direction of a single circle (havingone fixed radius), and the adjustment mechanism 9 for adjusting therelative position relationship between the center axis position of eachmounting hole 7 and the center position (center of gravity) of thecorresponding centrifugal pendulum 8.

In the rotary driving device 1 thus configured, it is possible to absorbvibration of the rotary driving device 1 produced when the driving motor4 is actuated to rotate the rotary shaft 2 about the axis thereof byoscillatory motion of the centrifugal pendulums 8 fitted in therespective mounting holes 7.

There can however be a case where an intended level of vibrationabsorbing effect is not obtained. In such a case, the relative positionrelationship between the center axis position of each mounting hole 7and the center position (center of gravity) of the correspondingcentrifugal pendulum 8 is to be finely adjusted so that the distance Lbetween the center position O1 of each centrifugal pendulum 8 whoseouter peripheral surface is in contact with the inner peripheral surfaceof the pertinent mounting hole 7 and the center axis position C1 of thepertinent mounting hole 7 would be varied. The distance L can be variedin this manner without varying the distance R between the center axisposition C1 of each mounting hole 7 and the center axis position C ofthe disk 6 as mentioned in the aforementioned equation (1) or withoutvarying the size of each centrifugal pendulum 8 (that is, by replacingthe disk 6 or the centrifugal pendulums 8). This approach makes itpossible to match the value of the natural frequency n of vibration ofthe centrifugal pendulums 8 with the frequency of vibration of therotary driving device 1 on a trial-and-error basis. Consequently, it ispossible to provide an improved vibration absorbing effect with respectto the vibration of the rotary driving device 1 by producing properoscillatory motion of the centrifugal pendulums 8.

Even after the disk 6 on which the mounting holes 7 are formed with thecentrifugal pendulums 8 loosely fitted in the mounting holes 7 is oncemounted on the rotary shaft 2, it is possible to effectively suppressthe vibration of the rotary driving device 1 by means of the adjustmentmechanism 9 on a trial-and-error basis as described above if a desiredvibration absorbing effect is not obtained. Therefore, unlike the caseof a conventional arrangement, it is not necessary to replace the disk 6or the centrifugal pendulums 8 with new ones when the desired vibrationabsorbing effect is not obtained. This makes it possible to prevent acost increase and an intricate task needed for replacing relevantcomponents.

The adjustment mechanism 9 a of the first embodiment shown in FIGS. 3A,3B, 4A and 4B includes the movable disk element 612 slidably mounted onthe rotary shaft 2 wherein the stationary disk element 611 has thestationary disk element side mounting holes 711 formed therein, each ofthe stationary disk element side mounting holes 711 constituting onepart of the mounting hole 71, and the movable disk element 612 has themovable disk element side mounting holes 712 formed therein, each of themovable disk element side mounting holes 712 constituting another partof the mounting hole 71.

In the first embodiment, the centrifugal pendulums 8 of the presentinvention are configured with the spherical bodies 81 having a diameterlarger than that of the mounting holes 71. The spherical bodies 81 aresandwiched between the stationary disk element 611 and the movable diskelement 612 with each of the spherical bodies 81 loosely fitted in eachpair of facing mounting holes 711, 712. The adjustment mechanism 9 aalso includes the locking member (screw B) for keeping the movable diskelement 612 from moving.

In the aforementioned structure, the movable disk element 612 is movedback and forth along the rotary shaft 2 to vary the distance between thestationary disk element 611 and the movable disk element 612 and, then,the movable disk element 612 is fixed by securing the locking member inposition. As the movable disk element 612 is fixed in this fashion, itis possible to vary the distance between the center axis of the rotaryshaft 2 and the center of gravity position of each spherical body 81when a centrifugal force produced by rotation of the rotary shaft 2about the center axis thereof is exerted on the spherical bodies 81. Itis possible to improve the vibration absorbing effect by finelyadjusting the aforementioned distance.

The movable disk element 612 has the outer cylindrical part 612 aprojecting in the axial direction of the rotary shaft 2 from a surfaceof the movable disk element 612 opposite to a surface thereof facing thestationary disk element 611. The outer cylindrical part 612 a has theslot 612 b formed therein, the slot 612 b extending along the axialdirection of the rotary shaft 2, and the rotary shaft 2 has the threadedhole 21 tapped into an outer peripheral surface of the rotary shaft 2 ata location corresponding to the slot 612 b. In this structure, the screwB screwed into the threaded hole 21 through the slot 612 b is used asthe aforementioned locking member.

Therefore, the movable disk element 612 can be moved back and forthalong the rotary shaft 2 upon loosening the screw B screwed into thethreaded hole 21 through the slot 612 b. Then, the movable disk element612 is set at a fixed position on the rotary shaft 2 if the screw B istightened after adjusting the distance between the stationary diskelement 611 and the movable disk element 612.

As the screw B is used as the locking member as discussed above, thelocking member can be made in a simple structure and the distancebetween the stationary disk element 611 and the movable disk element 612can be properly maintained in a reliable fashion.

The second embodiment shown in FIGS. 5A, 5B, 6A and 6C employs thetruncated conical bodies 82 as the centrifugal pendulums 8 of thepresent invention, each of the truncated conical bodies 82 fitted in oneof the mounting holes 72 gradually decreasing in diameter from one sideof the partially hollowed disk 62 toward the other side thereof. Each ofthe adjustment mechanisms 9 b includes the adjusting tab 91 fitted inone of the cutout spaces 65 formed in the partially hollowed disk 62 toconnect to one of the mounting holes 72, part of the adjusting tab 91being in contact with the tapered circumferential surface 821 of thepertinent truncated conical body 82, as well as the moving member(adjusting screw 92) for moving the adjusting tab 91 back and forth inthe pertinent cutout space 65 along the thickness direction of thepartially hollowed disk 62.

In the aforementioned structure, a contact point of each adjusting tab91 on the tapered circumferential surface 821 of the pertinent truncatedconical body 82 varies if each adjusting tab 91 is moved back and forthalong the axial direction of the rotary shaft 2 (that is, along thethickness direction of the partially hollowed disk 62) by manipulatingthe moving member. Thus, the center of gravity position of eachtruncated conical body 82 shifts in a radial direction of the partiallyhollowed disk 62 and, as a result, the distance between the center ofgravity position of each truncated conical body 82 and the center axisof the rotary shaft 2 varies. This makes it possible to finely adjustthe vibration absorbing effect.

In this structure, each of the adjusting screws 92 passed from one sideof the partially hollowed disk 62 to the opposite side thereof andscrewed into the adjusting tab 91 therethrough in the pertinent cutoutspace 65 is used as the moving member for moving the adjusting tab 91.It is possible to move each adjusting tab 91 back and forth along thethickness direction of the partially hollowed disk 62 by turning thepertinent adjusting screw 92 clockwise and counterclockwise about theaxis thereof.

As each of the adjusting screws 92 is used as the moving member asdiscussed above, the moving member can be made in a simple structure.

The third embodiment shown in FIGS. 7A, 7B, 8A and 8B employs theconical holes 73 as the mounting holes 7 formed in the thick-walled disk63 to pass therethrough, each of the conical holes 73 graduallydecreasing in diameter from one side of the thick-walled disk 63 towardthe other side thereof. Also, this embodiment employs the sphericalbodies 81 as the centrifugal pendulums 8, the diameter of each sphericalbody 81 is made larger than the minimum diameter of each conical hole 73and the thickness of the thick-walled disk 63.

The adjustment mechanism 9 c includes the positioning disk 94 which islocated face to face with the thick-walled disk 63 on one side thereofand mounted on the rotary shaft 2 movably along the axial directionthereof on the common axis with the rotary shaft 2, as well as thelocking member (screw B) for keeping the positioning disk 94 frommoving.

The adjustment mechanism 9 c thus configured keeps the spherical bodies81 from coming off the conical holes 73 with the aid of the positioningdisk 94 mounted face to face with the thick-walled disk 63 on one sidethereof where each conical hole 73 has the maximum diameter. In thisconfiguration, part of each spherical body 81 protrudes from thepertinent conical hole 73 toward the positioning disk 94.

The amount of projection of the spherical bodies 81 from thethick-walled disk 63 can be varied by moving the positioning disk 94back and forth along the axial direction of the rotary shaft 2. When thethick-walled disk 63 is caused to rotate about the rotary shaft 2integrally therewith, the distance between the center axis of the rotaryshaft 2 and the center of gravity position of each spherical body 81varies according to the amount of projection of the spherical bodies 81.This makes it possible to finely adjust the vibration absorbing effect.

The positioning disk 94 has the outer cylindrical part (projecting part)941 projecting along the axial direction of the rotary shaft 2 from asurface of the positioning disk 94 opposite to a surface thereof facingthe thick-walled disk 63. The outer cylindrical part 941 has the slot942 formed therein, the slot 942 extending along the axial direction ofthe rotary shaft 2. It is possible to securely fix the positioning disk94 to the rotary shaft 2 and thus position the spherical bodies 81 inthe respective conical holes 73 by tightening the screw B.

As the screw B which is passed through the slot 942 and screwed into thethreaded hole 21 is used as the locking member, the locking member canbe made in a simple structure.

An image forming apparatus 10 of the invention employing one of thecentrifugal pendulum vibration absorbers 51, 52, 53 of the foregoingfirst to third embodiments is now described with reference to FIGS. 9and 10. FIG. 9 is a perspective view showing the external appearance ofthe image forming apparatus 10 of the fourth embodiment, and FIG. 10 isa frontal cross-sectional view showing the internal construction of theimage forming apparatus 10. As depicted in FIGS. 9 and 10, the symbols−X/+X denotes a left-right direction and the symbols −Y/+Y denotes afront-rear direction. In particular, −X represents a leftward direction,+X represents a rightward direction, −Y represents a frontward directionand +Y represents a rearward direction.

The image forming apparatus 10 is a so-called internal exit tray typecopying machine having a main apparatus body 11. Referring to FIGS. 9and 10, the main apparatus body 11 includes an image forming section 12,a fixing section 13, a sheet storage section 14, a sheet dischargesection 15, an image reading section 16 and an operating section 17. Thesheet discharge section 15 is formed by creating a recessed portion inpart of the main apparatus body 11 beneath the image reading section 16.The image forming apparatus 10 is referred to as the internal exit traytype for this reason.

The main apparatus body 11 has a lower body portion 111 having agenerally parallelepipedic shape, a generally flat-shaped upper bodyportion 112 located above the lower body portion 111 face to facetherewith, and an interconnecting portion 113 located between the upperbody portion 112 and the lower body portion 111. The interconnectingportion 113 is a structural portion erected upright from a left part ofthe lower body portion 111 for joining the lower body portion 111 andthe upper body portion 112 to each other, forming the sheet dischargesection 15 therebetween. The upper body portion 112 is supported at aleft part thereof on an upper end part of the interconnecting portion113.

The image forming section 12, the fixing section 13 and the sheetstorage section 14 are provided inside the lower body portion 111, whilethe image reading section 16 is mounted in the upper body portion 112.In this embodiment, the operating section 17 is mounted to the upperbody portion 112 in such a manner that the operating section 17 juts outfrontward from a front end part of the upper body portion 112 as shownin FIG. 9.

The sheet storage section 14 includes a pair of upper and lower papercassettes 141 which can be removed from and inserted into the mainapparatus body 11. Each of these paper cassettes 141 holds a stack P1 ofprinting sheets (image carrying media) P. When executing an imageforming task (print job), the image forming apparatus 10 pulls out theprinting sheets P one after another and feeds each printing sheet P intothe image forming section 12 to carry out the image forming task.

The sheet discharge section 15 located between the lower body portion111 and the upper body portion 112 has an internal discharge tray 151formed on a top surface of the lower body portion 111. Each printingsheet P carrying a toner image transferred thereto is output from theimage forming section 12 and normally delivered onto internal dischargetray 151 from a lower part of the interconnecting portion 113.

The image reading section 16 includes contact glass 161 fitted in anupper opening of the upper body portion 112 for placing a document to bescanned, a document pressing cover 162 which can be swung up and downfor holding the document placed on the contact glass 161, and a scannermechanism 163 for scanning an image of the document placed on thecontact glass 161. Analog information concerning the document image readby the scanner mechanism 163 is converted into a digital signal which isoutput to a later-described exposure unit 123 for execution of the imageforming task.

The operating section 17 is for entering information concerning an imageforming task to be executed. The operating section 17 includes a powerswitch 170, numeric keys 171 and various other keys used for enteringthe number of prints to be produced on the printing sheets (printingmedia) P, for instance, a liquid crystal display (LCD) panel 172 usedfor entering information by touch-screen operation and displayingcomments, as well as a start key 173 used for initiating the imageforming task. When the start key 173 is pressed, the image formingapparatus 10 begins to scan the document image and carries out asequence of successive steps for performing the image forming task untila specified number of sheets P carrying toner images are output.

Provided on a right side of the lower body portion 111 immediately abovethe paper storage section 14 is a manual feed tray 18 which is mountedswingably on a pivot shaft 181 at a lower end so that the manual feedtray 18 can be flipped up and down between a closed position at whichthe manual feed tray 18 closes off a manual feed slot and an openposition at which the manual feed tray 18 projects in the rightwarddirection.

As illustrated in FIG. 10, there are provided a sheet convey unit 184and an interconnect unit 185 between the manual feed tray 18 and alater-described vertical paper convey path 101. The printing sheet Pmanually fed from the manual feed tray 18 is led into the vertical paperconvey path 101 through the sheet convey unit 184 and the interconnectunit 185 and guided along the vertical paper convey path 101 toward anipping part formed between a photosensitive drum (toner image carrier)121 and an image transfer roller 125 which will be described later.

A maintenance door 19 which can be opened and closed is provided on aleft side of the lower body portion 111 and an external discharge tray152 is provided immediately above the maintenance door 19 asillustrated. Upon completion of the print job, the printing sheet Pcarrying a printed image is ejected selectively onto the internaldischarge tray 151 or the external discharge tray 152.

The internal construction of the image forming apparatus 10 is describedin greater detail with reference to FIG. 10. As depicted in FIG. 10, theaforementioned photosensitive drum 121 is provided approximately at amiddle position of the image forming block 12. While the photosensitivedrum 121 rotates in a clockwise direction (as illustrated in FIG. 10)about a drum axis, an outer peripheral surface of the photosensitivedrum 121 is uniformly charged by a charging unit 122 which is locatedimmediately to the right of the photosensitive drum 121.

The exposure unit 123 produces a laser beam based on image informationrepresentative of the document image read by the image reading section16. The exposure unit 123 radiates the laser beam onto the outerperipheral surface of the photosensitive drum 121 to form anelectrostatic latent image thereon. As developer (hereinafter referredto as toner) is supplied from a developing unit 124 provided below thephotosensitive drum 121 to the electrostatic latent image subsequently,a toner image having the same pattern as the electrostatic latent imageis formed on the outer peripheral surface of the photosensitive drum121.

The printing sheet P supplied from one of the paper cassettes 141 of thesheet storage section 14 is fed along the vertically extending verticalpaper convey path 101 up to the photosensitive drum 121 on which thetoner image is formed through a pair of registration rollers 142 whichtogether serve to feed the printing sheet P with correct timing. Thetoner image on the outer peripheral surface of the photosensitive drum121 is transferred to the printing sheet P by the aforementioned imagetransfer roller 125 which is located to the left of the photosensitivedrum 121 face to face therewith. The printing sheet P carrying the tonerimage thus transferred is fed from the photosensitive drum 121 into thefixing section 13.

As the photosensitive drum 121 continues to rotate in the clockwisedirection upon completion of the aforementioned image transfer process,the outer peripheral surface of the photosensitive drum 121 is cleanedby a cleaning unit 126 which is provided immediately above thephotosensitive drum 121. Then, the outer peripheral surface of therotating photosensitive drum 121 is charged again by the charging unit122 in preparation of a succeeding image forming task.

The fixing section 13 has a housing accommodating a fixing roller 131having a built-in electric heating element, such as a halogen lamp, anda pressure roller 132 located to the left of the fixing roller 131 faceto face therewith. As the printing sheet P fed from the image formingsection 12 passes through a nipping part between the fixing roller 131and the pressure roller 132, the printing sheet P receives heat and, asa result, the toner image is fixed to the printing sheet P.

In the case of a single-sided print job, the printing sheet P carrying aprinted image on one side is ejected selectively onto the internaldischarge tray 151 in the sheet discharge section 15 or the externaldischarge tray 152 through a sheet discharge path 102 provided above thefixing section 13.

In the case of a double-sided print job, the printing sheet P carrying aprinted image on one side only is sent toward a temporary sheetaccommodating space 153, formed above the internal discharge tray 151,through a switchback paper convey path 103 which is provided above thesheet discharge path 102 up to a point where a forward half portion ofthe printing sheet P sticks out into the temporary sheet accommodatingspace 153. Then, the printing sheet P is fed in an opposite directionthrough a vertically extending reversing paper convey path 104 providedon the inside of the maintenance door 19 and fed again into the imageforming section 12 with the printing sheet P reversed for printing animage on a reverse side of the printing sheet P. Upon completion of thedouble-sided print job, the printing sheet P carrying the printed imageson both sides is discharged selectively onto the internal discharge tray151 or the external discharge tray 152.

The maintenance door 19 is provided with a cover member 191 which islocated immediately to the right of the reversing paper convey path 104,facing a left side of the image forming section 12. This cover member191 is held on a right side of the maintenance door 19. The verticalpaper convey path 101 for feeding the printing sheet P from one of thepaper cassettes 141 or the manual feed tray 18 is configured such thatpart of the vertical paper convey path 101 is located between a rightside of the cover member 191 and the left side of the image formingsection 12 under conditions where the cover member 191 is in a closedposition.

A reason why the maintenance door 19 is provided is as follows. If apaper jam occurs in part of the vertical paper convey path 101 locatedat the left side of the image forming section 12, a user (or servicepersonnel) can flip down the maintenance door 19 to an open position toexpose the vertical paper convey path 101 so that the printing sheet Pwhich has jammed can easily be located and removed.

The photosensitive drum 121 of the image forming apparatus 10 thusconfigured is an example of the rotary driving device 1 (FIG. 1) of thepresent invention, and the centrifugal pendulum vibration absorber 5(one of the centrifugal pendulum vibration absorbers 51, 52, 53,hereinafter referred to simply as the centrifugal pendulum vibrationabsorber 5 collectively) is applied to the photosensitive drum 121.Referring to FIG. 11 and other drawings where necessary, the centrifugalpendulum vibration absorber 5 employed in the photosensitive drum 121 isnow described hereinbelow.

FIG. 11 is a perspective view showing an example of a driving system 40of the photosensitive drum 121 and the centrifugal pendulum vibrationabsorber 5 applied to the photosensitive drum 121. The symbols −X/+X and−Y/+Y in FIG. 11 denote the same left-right and front-rear directions,respectively, as previously explained with reference to FIG. 9, −Xrepresenting the leftward direction, +X representing the rightwarddirection, −Y representing the frontward direction and +Y representingthe rearward direction.

As shown in FIG. 11, the photosensitive drum 121 has a drum shaft 121 apassing along the drum axis so that the photosensitive drum 121 canrotate integrally with the drum shaft 121 a on a common axis. The drumshaft 121 a is fitted rotatably about the axis thereof between front andrear unillustrated frames provided in the lower body portion 111 of themain apparatus body 11, whereby the photosensitive drum 121 is mountedat a specified position in the main apparatus body 11. The drum shaft121 a corresponds to the rotary shaft 2 of the earlier-described basicstructure and the first to third embodiments shown in FIGS. 1 to 8B.

The driving system 40 of the photosensitive drum 121 includes a drivingmotor 41 supported parallel to the front-rear direction by theunillustrated frame in the lower body portion 111, a driving gear 42having a small diameter mounted on a drive shaft 411 of the drivingmotor 41 on a common axis therewith so that the driving gear 42 canrotate integrally with the drive shaft 411, and a driven gear 43 havinga larger diameter than the driving gear 42 and mounted on the drum shaft121 a on a common axis therewith so that the driven gear 43 can rotateintegrally with the drum shaft 121 a, wherein dimensions of the drivinggear 42 and the driven gear 43 are so determined that the two gears 42,43 properly mesh with each other.

When the driving motor 41 is actuated, a driving force of the drivingmotor 41 is transmitted to the driven gear 43 via the drive shaft 411and the driving gear 42 with a turning speed of the driven gear 43reduced from that of the driving motor 41. Consequently, the driven gear43 rotates integrally with the drum shaft 121 a on the common axis,causing the photosensitive drum 121 to rotate. The driving gear 42 andthe driven gear 43 together constitute a mechanism corresponding to thegear mechanism 4 a of the basic structure of the rotary driving device 1shown in FIG. 1.

The centrifugal pendulum vibration absorber 5 of the present inventionis mounted between the driven gear 43 and the driving motor 41 at therear of the photosensitive drum 121 in such a manner that thecentrifugal pendulum vibration absorber 5 can rotate integrally with thedrum shaft 121 a on the common axis. The centrifugal pendulum vibrationabsorber 5 is mounted at the aforementioned location because it ispreferable that the centrifugal pendulum vibration absorber 5 be locatedas close as possible to the driving system 40, which is a source ofvibration, for effectively producing a vibration absorbing effect.Specifically, employed as the centrifugal pendulum vibration absorber 5is one of the centrifugal pendulum vibration absorbers 51, 52, 53 of theforegoing first to third embodiments shown in FIGS. 3A to 8B.

The centrifugal pendulum vibration absorber 5 is provided with theadjustment mechanism 9 on a rear side of the disk 6 for adjusting theradial position of each centrifugal pendulum 8. This arrangement makesit possible to easily adjust the radial position of each centrifugalpendulum 8 by means of the adjustment mechanism 9 from a rear side ofthe lower body portion 111. Specifically, employed as the adjustmentmechanism 9 is one of the adjustment mechanisms 9 a, 9 b, 9 c of theforegoing first to third embodiments shown in FIGS. 3A to 8B.

The photosensitive drum 121 of the image forming apparatus 10 is anexample of the rotary load body 3 shown in FIG. 1, and thephotosensitive drum 121 and the centrifugal pendulum vibration absorber5 together constitute the rotary driving device 1 of the presentinvention.

Since the photosensitive drum 121 is provided with the centrifugalpendulum vibration absorber 5 of this invention, vibration produced bythe driving system 40 when the same is operated is effectively absorbedby the centrifugal pendulum vibration absorber 5. Also, even if themounting holes 7 deviate from intended positions due to errors in designor manufacture or the driving system 40 vibrates in a state differentfrom what has been expected due to local conditions, for instance,pendular motion of the centrifugal pendulums 8 fitted in the mountingholes 7 can be properly controlled by finely adjusting the positions ofthe centrifugal pendulums 8 in radial directions by means of theadjustment mechanism 9. Thus, the centrifugal pendulum vibrationabsorber 5 can produce a sufficient vibration absorbing effect.Accordingly, the aforementioned arrangement of the invention makes itpossible to effectively prevent the occurrence of such an inconvenientsituation that an image can not be properly formed on the outerperipheral surface of the photosensitive drum 121 due to vibrationthereof.

It should be recognized that the invention is not limited to theforegoing embodiments but includes various modifications and variationsthereof as described hereinbelow, for example.

While the rotary driving device 1 shown in FIG. 1 includes the drivingmotor 4 and the gear mechanism 4 a mounted on one end of the rotaryshaft 2 and the centrifugal pendulum vibration absorber 5 mounted on theother end of the rotary shaft 2, the driving motor 4, the gear mechanism4 a and the centrifugal pendulum vibration absorber 5 may be mounted onthe same end of the rotary shaft 2. In this variation, the source ofvibration and a vibration absorbing part are located closer to eachother, making it possible to obtain a greater vibration absorbingeffect.

The centrifugal pendulum vibration absorbers 51, 53 of the first andthird embodiments include the adjuster 613 mounted between thestationary disk element 611 and the movable disk element 612 and betweenthe thick-walled disk 63 and the positioning disk 94, respectively. Theadjuster 613 is not absolutely necessary, however. It is possible toeliminate the adjuster 613 if the movable disk element 612 or thepositioning disk 94 is reliably mounted at a fixed position on therotary shaft 2 by securely tightening the screw B.

While the four mounting holes 7 are formed in the disk 6 (one of thedisks 61, 62, 63 of the first to third embodiments), the number of themounting holes 7 is not limited to four but may be less than or morethan four.

While the invention has been described with reference to theillustrative embodiment in which the image forming apparatus 10 havingthe photosensitive drum 121 applied with the centrifugal pendulumvibration absorber 5 is a copying machine, the image forming apparatus10 of the invention is not limited to the copying machine but may be aprinter which simply performs a print job based on image information fedfrom an external apparatus like a computer or a facsimile machine whichperforms a print job based on image information fed through acommunications line, for example.

While the printing sheet P used as an image carrying medium in the imageforming apparatus 10 of the foregoing embodiment is a sheet of paper,the image carrying medium is not limited to the sheet of paper in thisinvention. For example, the image carrying medium may be a transparentplastic sheet used in an overhead projector or an image transfer belt towhich toner images of different colors once formed on the outerperipheral surface of the photosensitive drum 121 are transferred forcolor printing. In the latter case, the color images transferred to theimage transfer belt one on top of another are eventually togetherretransferred to a sheet of paper or a transparent plastic sheet.

While the invention has thus far been described with reference to theillustrative embodiments thereof, principal arrangements and features ofthe invention can be summarized as follows.

In one preferable form of the invention, a rotary driving deviceincludes a rotary shaft supported rotatably about an axis thereof on apredetermined supporting member, a rotary load body mounted on therotary shaft to project radially outward from the rotary shaft in such amanner that the rotary load body can rotate integrally with the rotaryshaft about the axis thereof, a driver for rotating the rotary shaftabout the axis thereof, a disk mounted on the rotary shaft coaxiallytherewith for integral rotation with the rotary shaft, the disk having amounting hole formed therein, a pendulum loosely fitted in the mountinghole, and an adjustment mechanism for adjusting a relative positionrelationship between a central axis position of the mounting hole and acenter of gravity position of the pendulum under conditions where thedisk is rotating.

According to the rotary driving device thus configured, the disk rotatesabout the rotary shaft concentrically therewith when the driver isactuated, so that vibrational energy of the rotary driving device isabsorbed by pendular motion (oscillatory motion) of the pendulum fittedin the mounting hole formed in the disk. This serves to suppressvibration of the rotary driving device. If the oscillatory motion of thependulum does not produce an initially intended level of vibrationabsorbing effect, the relative position relationship between the centralposition of the mounting hole and the center of gravity of the pendulumis varied by manipulating the adjustment mechanism and the vibrationabsorbing effect thus produced is reconfirmed repetitively on atrial-and-error basis. By this adjustment process, it is possible tomake the frequency of vibration of the rotary driving device equal tothe natural frequency of vibration of the pendulum, so that oscillatorymotion of the rotary driving device is effectively absorbed.

Also, even after the disk having the mounting hole in which the pendulumis loosely fitted is once mounted on the rotary shaft, it is possible toeffectively suppress vibration of the rotary driving device bymanipulating the adjustment mechanism if the desired vibration absorbingeffect is not obtained. Therefore, unlike the case of a conventionalarrangement, it is not necessary to replace the disk or the pendulumwith new ones when the desired vibration absorbing effect is notobtained. This makes it possible to effectively prevent the occurrenceof such an inconvenient situation that replacement of components resultsin a cost increase. Additionally, as one can quickly enhance vibrationabsorbing performance according to the structure of the invention, it ispossible to ensure that the rotary driving device constantly producesthe desired vibration absorbing effect.

In the rotary driving device of the above structure, preferably, thecentral axis of the mounting hole is set to be parallel to the axis ofthe rotary shaft, the pendulum is caused to move radially outward withinthe mounting hole due to a centrifugal force produced by rotary motionof the disk, and the adjustment mechanism adjusts the relative positionrelationship between the central axis position of the mounting hole andthe center of gravity position of the pendulum under conditions wherethe pendulum is moved radially most outward in the mounting hole.

In the rotary driving device of the above structure, preferably, theadjustment mechanism goes into contact with the pendulum to regulate theamount of radially outward movement of the pendulum within the mountinghole, thereby adjusting the relative position relationship between thecentral axis position of the mounting hole and the center of gravityposition of the pendulum.

The following description deals with specific arrangements for adjustingthe relative position relationship between the central axis position ofthe mounting hole and the center of gravity position of the pendulum.

In the rotary driving device of the above structure, preferably, thedisk includes a stationary disk element fixedly mounted on the rotaryshaft and a movable disk element slidably mounted on the rotary shaft,the mounting hole is made of a first mounting hole formed in thestationary disk element and a second mounting hole formed in the movabledisk element so as to accommodate the pendulum between the first andsecond mounting holes, the pendulum is a spherical body having adiameter larger than a minimum diameter of the mounting hole and thespherical body is fitted in the mounting hole while being sandwichedbetween the stationary disk element and the movable disk element, andthe adjustment mechanism includes the movable disk element sliding onthe rotary shaft to go into contact with the pendulum through the secondmounting hole and a locking member keeping the movable disk element frommoving.

According to the rotary driving device thus configured, the distancebetween the stationary disk element and the movable disk element varieswhen the movable disk element is moved back and forth along the rotaryshaft. It is therefore possible to vary the distance between the centralaxis of the rotary shaft and the center of gravity of the pendulum underconditions where the centrifugal force produced by rotation of therotary shaft is exerted on the spherical body sandwiched between thestationary and movable disk elements. It is possible to improve thevibration absorbing effect by adjusting the distance between the twodisk elements in the aforementioned fashion.

In the rotary driving device of the above structure, preferably, themovable disk element includes a facing surface facing the stationarydisk element, an opposite surface opposite to the facing surface and aprotrusion part protruding from the opposite surface in a direction inwhich the rotary shaft extends, the projecting part has a slot so formedas to extend in the direction in which the rotary shaft extends, therotary shaft has a peripheral surface formed with a threaded holecorresponding to the slot, and the locking member is a screw screwedinto the threaded hole through the slot.

According to the rotary driving device thus configured, the movable diskelement can be moved back and forth along the rotary shaft uponloosening the screw screwed into the threaded hole through the slotformed in the projecting part of the movable disk element. Then, themovable disk element is set at a fixed position on the rotary shaft ifthe screw is tightened after adjusting the distance between thestationary disk element and the movable disk element.

As the screw is used as the locking member as discussed above, thelocking member can be made in an extremely simple structure and thedistance between the stationary disk element and the movable diskelement thus adjusted can easily be maintained.

In the rotary driving device of the above structure, the disk has oneand the other surfaces facing in opposite directions, the pendulum is atruncated conical body having a tapered peripheral surface that has adiameter gradually decreasing from the one surface toward the othersurface, the disk has a cutout space formed therein by cutting out aportion of the disk from an outer peripheral surface thereof toward themounting hole, and the adjustment mechanism includes an adjusting tabmounted in the cutout space and going into contact with the taperedperipheral surface of the truncated conical body and a moving membermoving the adjusting tab back and forth along a thickness direction ofthe disk.

According to the rotary driving device thus configured, a contact pointof the adjusting tab on the tapered circumferential surface of thetruncated conical body varies if the adjusting tab is moved back andforth along the axial direction of the rotary shaft (that is, along thethickness direction of the disk) by manipulating the moving member dueto the centrifugal force produced by rotation of the disk about therotary shaft. As a result, the center of gravity position of thetruncated conical body moves along a radial direction of the disk andthe distance between the center of gravity position of the truncatedconical body and the central axis of the rotary shaft varies. This makesit possible to finely adjust the vibration absorbing effect of therotary driving device.

In the rotary driving device of the above structure, preferably, themoving member is an adjusting screw passing through the disk from theone surface to the other surface while passing through the adjusting tabmounted in the cutout space.

According to the rotary driving device thus configured, the adjustingtab can be moved back and forth along the thickness direction of thedisk by turning the adjusting screw clockwise and counterclockwise aboutan axis thereof. It is possible to make the moving member in a simplestructure by using the adjusting screw as the moving member as mentionedabove.

In the rotary driving device, preferably, the disk has first and secondsurfaces facing in opposite directions, the mounting hole is a conicalhole having a diameter gradually increasing from the first surfacetoward the second surface, the pendulum is a spherical body having adiameter larger than both a minimum diameter of the conical hole and thethickness of the disk, and the adjustment mechanism includes apositioning disk arranged in face to face relation with the secondsurface and slidably and coaxially fitted on the rotary shaft and alocking member keeping the positioning disk from moving.

This configuration serves to keep the spherical body from coming off theconical hole with the aid of the positioning disk mounted face to facewith the first surface of the disk where the conical hole has theminimum diameter. In this condition, part of the spherical bodyprotrudes from the conical hole toward the positioning disk.

The amount of projection of the spherical body from the conical hole inthe disk can be varied by moving the positioning disk along the axialdirection of the rotary shaft. Thus, when the disk is caused to rotateabout the rotary shaft integrally therewith, the distance between thecenter axis of the rotary shaft and the center of gravity position ofthe spherical body varies according to the amount of projection of thespherical body. This makes it possible to finely adjust the vibrationabsorbing effect of the rotary driving device.

In the rotary driving device of the above structure, preferably, thepositioning disk includes a facing surface facing the disk, an oppositesurface opposite to the facing surface and a protrusion part protrudingfrom the opposite surface in a direction in which the rotary shaftextends, the projecting part has a slot so formed therein as to extendin the direction in which the rotary shaft extends, the rotary shaft hasa peripheral surface formed with a threaded hole corresponding to theslot, and the locking member is a screw screwed into the threaded holethrough the slot.

In the rotary driving device thus configured, it is possible to affixthe positioning disk to the rotary shaft and thereby set the sphericalbody in position by tightening the screw fitted in the threaded hole inthe rotary shaft. Since the screw is screwed into the threaded hole inthe rotary shaft through the slot in the projecting part of thepositioning disk, it is possible to move the positioning disk back andforth along the axial direction of the rotary shaft. As the screw isused as the locking member as discussed above, the locking member can bemade in a simple structure.

What is claimed is:
 1. A rotary driving device comprising: a rotaryshaft supported rotatably about an axis thereof on a predeterminedsupporting member; a rotary load body mounted on the rotary shaft toproject radially outward from the rotary shaft in such a manner that therotary load body can rotate integrally with the rotary shaft about theaxis thereof; a driver for rotating the rotary shaft about the axisthereof; a disk mounted on the rotary shaft coaxially therewith forintegral rotation with the rotary shaft, the disk having a mounting holeformed therein, the mounting hole being aligned along a central axis setparallel to the axis of the rotary shaft; a pendulum loosely fitted inthe mounting hole, the pendulum being caused to move radially outwardwithin the mounting hole due to a centrifugal force produced by rotarymotion of the disk on the rotary shaft; and an adjustment mechanism foradjusting a relative position relationship between a central axisposition of the mounting hole and a center of gravity position of thependulum under conditions where the pendulum is moved radially mostoutward in the mounting holes; wherein the disk has first and secondsurfaces facing in opposite directions, wherein the mounting hole is aconical hole having a diameter gradually increasing from the firstsurface toward the second surface, wherein the pendulum is a sphericalbody having a diameter larger than both a minimum diameter of theconical hole and the thickness of the disk, and wherein the adjustmentmechanism includes a positioning disk arranged in face to face relationwith the second surface and slidably and coaxially fitted on the rotaryshaft and a locking member keeping the positioning disk from moving. 2.The rotary driving device according to claim 1, wherein the positioningdisk includes a facing surface facing the disk, an opposite surfaceopposite to the facing surface and a protrusion part protruding from theopposite surface in a direction in which the rotary shaft extends, theprojecting part having a slot so formed therein as to extend in thedirection in which the rotary shaft extends, wherein the rotary shafthas a peripheral surface formed with a threaded hole corresponding tothe slot, and wherein the locking member is a screw screwed into thethreaded hole through the slot.
 3. An image forming apparatuscomprising: a photosensitive drum driven to rotate about a drum axis andhaving a peripheral surface on which an electrostatic latent image isformed based on image information and then a toner image having the samepattern as the electrostatic latent image is formed, the photosensitivedrum transferring the toner image to an image carrying medium whilerotating about the drum axis; and a rotary driving device for drivingthe photosensitive drum to rotate, the rotary driving device including:a rotary shaft supported rotatably about an axis thereof on apredetermined supporting member and supporting rotatably thephotosensitive drum for integrally rotation; a driver for rotating therotary shaft about the axis thereof; a disk mounted on the rotary shaftcoaxially therewith for integral rotation with the rotary shaft, thedisk having a mounting hole formed therein, the mounting hole beingaligned along a central axis set parallel to the axis of the rotaryshaft; a pendulum loosely fitted in the mounting hole, the pendulumbeing caused to move radially outward with the mounting hole due to acentrifugal force produced by rotary motion of the disk on the rotaryshaft; and an adjustment mechanism for adjusting a relative positionrelationship between a central axis position of the mounting hole and acenter of gravity position of the pendulum under conditions where thependulum is moved radially most outward in the mounting holes; whereinthe disk has first and second surfaces facing in opposite directions,wherein the mounting hole is a conical hole having a diameter graduallyincreasing from the first surface toward the second surface, wherein thependulum is a spherical body having a diameter larger than both aminimum diameter of the conical hole and the thickness of the disk, andwherein the adjustment mechanism includes a positioning disk arranged inface to face relation with the second surface and slidably and coaxiallyfitted on the rotary shaft and a locking member keeping the positioningdisk from moving.
 4. The image forming apparatus according to claim 3,wherein the positioning disk includes a facing surface facing the disk,an opposite surface opposite to the facing surface and a protrusion partprotruding from the opposite surface in a direction in which the rotaryshaft extends, the projecting part having a slot so formed therein as toextend in the direction in which the rotary shaft extends, wherein therotary shaft has a peripheral surface formed with a threaded holecorresponding to the slot, and wherein the locking member is a screwscrewed into the threaded hole through the slot.